Synthesis of Chloroform

With Calcium Hypochlorite and Acetone

When chlorine is passed into boiling alcohol, both chlorination of the methyl group and oxidation of the primary alcohol group to an aldehyde occur, giving trichloro-acetaldehyde or chloral: When chloral is treated with caustic alkali, fission of the C-C linkage occurs, giving chloroform and a formate. Acetaldehyde and also many ketones, such as acetone, containing the CH3CO- group behave similarly when treated with calcium or sodium hypochlorite, chlorination of the CH3CO- group being immediately followed by fission of the molecule by the alkali present in the hypochlorite solution. The acetone method clearly gives a much cheaper product than the alcohol method.

Required: Calcium Hypochlorite 100g (bleaching powder), acetone 44ml

Place 100g of calcium hypochlorite in a mortar and add 250 ml of water in small quantities at a time: between each addition grind the mixture of bleaching powder and water well together and decant the cream-like suspension through a funnel into a 1-litre flat-bottomed flask. Finally, when all the water has thus been used, only a gritty residue remains in the mortar. Fit the flask with an efficient reflux water-condenser, pour 44ml (35g) of acetone in small quantities, at a time, down the condenser and mix by thorough shaking after each addition. The reaction usually starts spontaneously after a few minutes, and a bath of cold water should be available into which the flask may be dipped if necessary to moderate the reaction. Should the reaction show no signs of starting within 5 minutes of the addition of the acetone, warm the flask cautiously on a boiling water-bath until the reaction starts, and then remove it immediately. When the vigorous boiling has subsided, heat the flask on a boiling water-bath for a further 5-10 minutes (not more) to complete the reaction. Cool the flask in cold water (to prevent loss of chloroform vapour whilst the apparatus is being rearranged) and then fit the flask with a fairly wide delivery-tube and reverse the water-condenser for distillation. Heat the flask on a water-bath until distillation of the chloroform is complete.

The chloroform thus obtained is usually acidic. Therefore shake it thoroughly with dilute sodium hydroxide solution in a separating-funnel. (If the chloroform tends to float on the alkaline solution, it still contains appreciable quantities of acetone: in this case the soda should be run out of the funnel and the chloroform shaken with water to extract the acetone. The extraction with the soda can then be performed after the water has been removed.) Carefully run off the heavy lower layer of chloroform into a small conical flask, dry it over calcium chloride for 15-20 minutes, and then filter it directly into a 75 ml. distilling-flask fitted with a clean dry water-condenser. Distill the chloroform, collecting the fraction of bp. 60-63øC. Yield, 30g. (20ml).

Chloroform is a colourless liquid, of bp 61ø and d 1.50. It has a characteristic sweetish smell, and is frequently used as a solvent in organic chemistry.

Reference: Mann & Saunders, Practical Organic Chemistry, 3rd Ed

Go get a five gallon bucket. The ones used for painting work well and are available new, with a cover, in the paint department of most big homeowner stores. The cover can be used to keep bird droppings and bugs out of the reaction. Put the bucket outside in a reasonably ventilated area with good drainage away from any shrubbery that can be killed by spills. Pour two gallons of 10% sodium hypochlorite solution into the bucket. This material is available in two one-gallon containers for around $4.00 from the local homeowner store in the swimming pool section labeled, "Liquid Pool Chlorine." Make sure you get the Sodium Hypochlorite, not the Hydrochloric Acid that's in the same section, HCl is useful, but not for this reaction.

Add 5 pounds of ice to the Hypochlorite. Be careful pouring this stuff, it's bleach, but twice as strong as the stuff Mom uses to do your laundry. Each splash on your clothing will eat a nice white hole. Stir with a plastic or wooden spoon, avoid metal. Metal spoons won't spoil the reaction, but it may spoil the spoon.

While the solution cools, measure out 340 grams of acetone into a container. Add about half of the measured acetone into the ice solution and stir it up. Wait about 10 minutes and feel the side of the bucket. It should feel warmer near the bottom and colder as you raise your hand to the ice. Stir the ice mix around and equalize the temperature. Add the rest of the acetone and stir again. Let it set for about 10 minutes.

If you didn't listen and used less than five pounds of ice in the solution, it will get hot enough to boil off the Chloroform and leave you with nothing but a bad smell, splatters where it boiled over and probably holes in your shoes and clothes. As a matter of fact it would be good to have an extra five pounds of ice around in case you're doing this in the middle of the day in Panama where the temperature is hovering around 104F. At this temperature, or if you're doing this in the Peruvian Mountains at 6500 feet it may take more ice to keep it cool enough not to boil off the Chloroform as it forms. This is a very exothermic reaction, but it can be controlled easily by the addition of ice as needed.

You should have a cool mixture of ice and something that is starting to look cloudy. It will be colder on the top than the bottom and most of the ice has melted. Let this mixture set until the ice completely melts. Grab the bucket and carefully pour off the water and fine white powder leaving behind the Chloroform that has settled to the bottom of the bucket. When you're pouring off the water, it may be hard to see the Chloroform, but trust me, it's in there. The Chloroform is heavier than water and falls to the bottom in a bubble looking blob. The blob will have a white powder clinging to it. Just pour off the water until you can clearly see the blob and then pour blob, water and powder into a smaller, easier to handle container. There may be some bubbles forming and rising to the top of the solution. Don't worry, this is normal and will not cause a problem…unless you try to seal the reactants up.

Pour the Chloroform, powder and water through a coffee filter into a separatory funnel and separate the crude Chloroform, which will sink to the bottom. You will get around 200ml of crude Chloroform. Disappointed? This reaction uses very cheap materials and is one of the simplest, cheapest methods known, so just quit bitching and deal with it. Since the procedure is so simple up to this point, make a few more batches before moving to the next step.

The Chloroform has water and the white powder still in it and this needs to be removed. The Chloroform can be vacuum filtered through a six inch sand filter to remove the powder and then passed through about 4 inches of anhydrous magnesium sulfate to remove most of the water, but the mechanical loss would kill half of the product. The best way to clean this up is to distill it. Use an appropriately sized flask, a one liter two-necked flask will work well, even for larger volumes. If you're doing more than half a liter, pour it in as the distillation progresses. Use a fractionating column, I use a 400mm, set up for normal distillation with an oil bath and magnetic stirring. If this last paragraph doesn't mean a thing to you, go to the library and get an organic lab survivor's guide. These books have pictures and complete descriptions of all the pieces I'll talk about.

Remember, distilling Chloroform is not an incredibly safe procedure. Chloroform fumes are toxic and narcotic, and may knock you out if aren't being careful. On contact with flames and hot surfaces it can decompose into the dangerous war gas phosgene. So ventilate the area with fans to remove the vapors and attach a vent tube to the vacuum adapter that leads away from the area where you're working.

It is interesting watching Chloroform distill through a fractionating column. As the solution comes to a boil a gray cloud rises up the column until it reaches the distilling head and spills into the condenser where it disappears into fluid. Below the rising cloud the Chloroform condenses on the sides of the column and drips back into the solution to be converted into the rising cloud again. Keep the boil fairly slow, you don't want to boil it dry while you're off visiting the bathroom or kitchen. The first Chloroform that comes over is tainted with water, don't worry about it, keep collecting. When the Chloroform is almost gone from the source flask, add about 200 ml of water and bring to a gentle boil to force the remaining Chloroform from the column (there's a bunch of stuff in there). You can tell when the Chloroform is done because the temperature starts to rise pretty quickly from 60c to 80c. Stop the distillation at this point.

As the Chloroform distilled it azeotropically carried over some water that can now be seen as clear bubbles clinging to the sides of the receiving flask or floating around on the top of the clear Chloroform. It can also cloud up the Chloroform some. Pour the Chloroform into a separatory funnel. Put a flask fitted with a filtering funnel loaded with a couple of inches of anhydrous Magnesium Sulfate under the separatory funnel, and let the Chloroform slowly drain through while separating the water. This will leave you with clear anhydrous Chloroform in the flask.

To make anhydrous Magnesium Sulfate, get some Epsom Salts at the drug store and pour about a pound into a casserole dish. Heat the casserole dish in the oven at 450F for about 4 hours. After cooling and chipping and crushing the fused material you have anhydrous Magnesium Sulfate. Putting it in a thick plastic bag and tapping gently with a hammer can crush this stuff. Use a butter knife to get it out of the pan, not an ice pick! You can also line the pan with aluminum foil to make removal easier, but sometimes it's hard to get the aluminum loose from the Magnesium Sulfate. Don't grease the pan stupid!

Now look back at what's left in the distilling flask. It's got water and some nasty green stuff clinging to the sides and a white powder setting on the bottom. See why you distilled it? This crud would have been left in the chloroform and screwed up everything you used it for.

Put your crystal clear, anhydrous Chloroform in a brown bottle, cap tightly and store away from light. If you're going to store it for a long time put a couple of drops of 95% alcohol in to stabilize it. Warning, Chloroform will eat rubber, so don't use a rubber stopper. Glass or teflon seals are the best.

Chromic: Corrections to Cheapskates chloroform writeup (update 9/9/02)

Cheapskate messed up in his calculations in http://rhodium.ws/chemistry/chloroform.html. This is certainly not an uncommon mistake, as I too messed up the corrections before this update!

6 mol OCl- is required for 1 mol acetone. Depending on the source of hypochlorite, the overall reaction is:

• CH3COCH3 + 6 NaOCl -> CHCl3 + NaCH3COO + 2 NaOH + 3 NaCl
• 2 CH3COCH3 + 6 Ca(OCl)2 -> 2 CHCl3 + (CH3COO)2Ca + 2 Ca(OH)2 + 3 CaCl2

To repeat the calculations with Cheapskate's original scale of 340g of acetone, that is 431.5mL or 5.85mol of acetone. 5.85mol of acetone requires 6x the equiv of NaOCl, or 35.12mol of NaOCl. That is 2.613kg of pure crystalline NaOCl, or 24.197kg of 10.8% NaOCl (52.264kg of 5% NaOCl).

10% NaOCl has a density of 1.16g/mL. So that is a volume of 20.9L of NaOCl. Or 5.52 U.S. gallons (1gal = 3.78L). Cheapskate is using 2 gallons, ie he is only using 36% of the amount he should be using (it's a surprise he made any chloroform!).

However, where I live, bleach is sold in 4L containers... so all this makes no sense to me anyways! So I'll redo the calculations.

The final word is: For every 1g of acetone (1.27mL) you want to oxidize, use 71.2g (61.4mL) of 10.8% NaOCl (142.3g of 5% NaOCl).

Also, if you're having trouble oxidizing anything with NaOCl, use 1-2 mol of HCl to 1 mol of acetone required, and drip it in with what you're oxidizing. Ie, if you want to make sure the NaOCl oxidizes the acetone easily, add 1-2 mol eq's of 31% HCl relative to the acetone, and drip the acetone/HCl into the mixture slowly. If you're not using acid, the reaction hardly comes to reflux (a condenser or some cooling is needed though).

Beware, if you use too little bleach, this is a fast exothermic reaction as Cheapskate wrote about. Distillation of chloroform is not anything to be worried about, no more so than methylene chloride or any other chlorinated solvent. There is no need for a fractionating column when distilling all of the acetone is gone, but do add some ethanol as Cheapskate indicates! Good luck with the Reimer-Tiemann formylation!

Data I used for the calculations:

• 10.8% NaOCl (w/w)
• 31.25% HCl(aq) (w/w)
• 0.03646 g/mmol HCl
• 0.0744 g/mmol NaOCl
• 0.05808 g/mmol acetone
• 0.788 g/mL acetone
• 1.16 g/mL 10.8% bleach
• 1.08 g/mL 5% bleach

Chloroform, if stored for more than a few months, decomposes to Phosgene; which as you know was a WW1 era chemical weapon. To prevent this, small amounts of methanol should be added to the Chloroform to prevent it from decomposing to Phosgene. Also, I think it is worth warning the reader that if the reaction between Calcium Hypochlorite and Acetone is not cooled properly, it may produce Phosgene. Have a good day.

-Tariq